Processes for producing lower aliphatic monocarboxylic acids such as acetic acid by the vapor phase oxidation of lower aliphatic hydrocarbons are known. For example, acetic acid is prepared by the vapor phase oxidation of butane according to the following equation: EQU C.sub.4 H.sub.10 + 5/2 O.sub.2 .fwdarw.2CH.sub.3 COOH+H.sub.2 O.
However, processes for the oxidation of hydrocarbons in the vapor phase by means of oxygen-containing gases have not proven entirely satisfactory primarily due to the excessive formation of undesirable carbon oxides, and to the difficulty in maintaining control of the highly exothermic oxidation reaction. U.S. Pat. No. 3,395,159 provides an improved process wherein the oxidation of hydrocarbons is performed in a reactor system having fused vanadium oxide catalyst coated on the inner surface of the reactor, which system has the advantage of better temperature control and isothermal operation. The use of early catalysts, such as vanadium pentoxide, either supported or unsupported, for the vapor phase oxidation of lower aliphatic hydrocarbons generally results in yields and process efficiencies which fall substantially short of economic potential. Also, the resulting products are often impure due to a lack of selectivity when such catalysts are employed.
In copending applications Ser. Nos. 859,896; 859,595 and 859,898 catalyst and catalytic processes have been presented which realize superior results in the vapor phase oxidation of lower aliphatic hydrocarbons especially n-butane, however as with all catalytic processes there is always a desire to increase selectivity to the preferred product as opposed to the attendant less desired by-products and to reduce oxidation of the catalyst which oxidation is a negative feature of the instant high pressure reactor process which utilizes an activated catalyst in reduced form.